Puffed rice reveals patterns in compressed porous materials

An international research team has presented a creative approach to explaining the patterns of movement in porous materials when compressed. Their study, which made use of puffed rice cereal, has been published in the journal Nature Physics.

Lead author Professor Itai Einav, from the University of Sydney’s Particles and Grains Laboratory, has the long-term research objective of understanding how grains behave under varying conditions. Professor Einav said he and his team “knew that brittle porous materials such as rocks, foams or even snow exhibit irreversible compaction patterns… [but] what we didn’t know is in what ways it moves and deforms, and specifically what types of internal patterns develop”.

Professor Einav and his team, from the University of Sydney and San Diego State University, decided to use puffed rice in order to demonstrate this movement. He explained, “We picked puffed rice because they are highly porous and compliant and typify generic brittle porous materials when being compressed.

“We wanted to understand how packs of brittle grains coordinate motion when crushed. Many of us have tried this at home as kids — crushing puffed rice cereal with a spoon.

“For us, this simple experiment revealed surprisingly rich compaction patterns that were due to the competing processes of internal collapse and recovery.”

Co-lead author Dr François Guillard, also from the University of Sydney, said the research model replicating the experiments offers a new perspective on jerky flows in metallic alloys.

“We used a robust spring-lattice model to capture the process of internal collapse and recovery and are now able explain the dynamics of previously and newly observed patterns,” he said.

The results of the research will have an impact on our understanding of everything from snowballs colliding during avalanches to crater patterns formed during meteorite impacts. Dr Guillard said, “The lattice model we have created can address other brittle porous media such as natural rocks, bones and snow, and man-made ceramics, foams and pharmaceutical powders.”

Image caption: Itai Einav and François Guillard test their theory in a coffee pot.